Lightly coat bottom of a 13x9 inch pan with cooking spray. In a saucepan over medium heat, melt cheese and butter together, then add peanut butter and stir until smooth. Remove from heat; add vanilla and nuts. Place confectioners' sugar in a large bowl. Pour cheese mixture over sugar. Stir until completely mixed. Candy will be very stiff. Using your hands, remove candy from bowl and press evenly and firmly into pan. Pat top of candy with a paper towel to remove excess oil. Place pan in refrigerator until candy is firm, about 1 hour. Fudge will keep, covered with plastic wrap, for up to 1 week. To serve, cut fudge into small squares, about 64 total.